Answer:Artificial light from cities has created a permanent "skyglow" at night, obscuring our view of the stars. Here's their map of artificial sky brightness in North America, represented as a ratio of "natural" nighttime sky brightness. In the black areas, the natural night sky is still (mostly) visible.
Explanation:
<span>Various gases and liquids have different densities and combustion points.</span>
Mitosis makes new cells and replaces the cells that are old, lost or damaged
